New Treatment 'Roadmap' Improves Odds for Unusual Brain Aneurysm

A six-year study of a special type of brain aneurysm -- the thrombotic
aneurysm -- has led to a treatment "roadmap" that should mean better outcomes
for patients with this unusual medical problem.

UCSF Medical Center neurosurgeon Dr. Michael Lawton headed the clinical
research team. The findings are reported in the March 2005 issue of
Neurosurgery.

Approximately 5 percent of the U.S. population develops a brain aneurysm at
some time, and an even smaller percentage -- about 0.5 percent -- is diagnosed
with a thrombotic aneurysm. An aneurysm is an outpouching or bulge in an artery
that usually forms at a branch point. The bulge represents a weakened spot in
the
arterial wall, and without treatment there is a risk of hemorrhage leading to
brain damage or death. A thrombotic aneurysm is unusual because it contains a
blood clot.

In surgical treatment for a brain aneurysm, tiny metal clips, something like
tiny clothespins, are typically used to separate the aneurysm from the normal
vessel. The clips keep blood from entering the aneurysm, and as a result future
bleeding is prevented and nearby brain tissue is protected. A solid clot inside
the aneurysm makes it difficult for the blades of the clip to squeeze the
aneurysm and make the separation from the normal vessel.

In an attempt to develop better ways to treat patients with thrombotic
aneurysms, the research team studied 68 patients with the disorder. The
researchers developed a classification system of six different types of
thrombotic aneurysms and the best way to treat each type.

At UCSF Medical Center, surgeons perform more than 400 brain aneurysm
procedures a year, and while all are not thrombotic, when this type does arise
it presents particular challenges to a neurosurgeon, according to Lawton.

"When confronted with a thrombotic aneurysm, the neurosurgeon's instinct to
clip collides with the solid mass of the aneurysm forcing him or her to trap
the aneurysm between temporary clips...," the researchers write in
the journal article. The next steps are to open the aneurysm wall, remove the
blood clot from inside the aneurysm, and then reconstruct the neck of the
aneurysm with clips. "This technique is stressful and the outcome
unpredictable," they add, and can be associated with prolonged interruption of
blood flow to the brain (known as ischemia), failed reconstructions, and poor
results.

The study sought to address this with a classification system, giving the
neurosurgeons more information on how to proceed with these challenging cases,
Lawton said.

"There is little time to waste when a patient presents with an aneurysm,"
Lawton said. "The classification scheme may provide important preoperative
guidance to neurosurgeons, increasing the chances of preserving the patient's
life and function."

Lawton likened the classification to a driver having a roadmap. "It puts the
surgeon a couple of steps further ahead," he said.

All of the patients in the study had surgery performed by Lawton. There were 41
women and 27 men who ranged in age from 11 to 79 years old, with a mean age of
53. The aneurysm types were assigned by the other study investigators on the
basis of preoperative radiographic studies independent of findings during
surgery.

An important finding of the study was that, despite their solid mass, one-third
of thrombotic aneurysms can be treated surgically with conventional clipping,
the researchers noted.

In addition, the researchers discovered that patients with unclippable
thrombotic aneurysms had more favorable results when treated with bypass and
occlusion, rather than with thrombectomy (removal of the clot) and
reconstruction of the parent arteries with clips. With aneurysm occlusion, the
surgical team completely shuts down the affected artery, but in order to do
that safely, blood flow is first rerouted around the aneurysm with a bypass. In
a bypass procedure, a blood vessel is taken from another part of the body,
usually the leg, and is grafted to a brain artery downstream from the aneurysm
to maintain blood flow to that territory. This treatment therefore eliminates
blood flow through an aneurysm while preserving flow to normal brain.

The journal report details, through description and illustration, the six
classifications of thrombotic aneurysms. The aneurysms range from Type 1, which
is the classic thrombotic aneurysm, to Type 6, in which the aneurysm was
previously treated with implantation of coils. These tiny platinum coils are
deployed into the aneurysm to block blood flow and prevent rupture.

Along with Lawton, authors of the paper include Dr. Alfredo Quinones-Hinojosa,
and Dr. Edward Chang, both residents in neurosurgery, UCSF Medical Center; and
Dr. Timothy Yu, Department of Neurology, Massachusetts General Hospital,
Harvard Medical School.